Scientists at Sheffield Hallam University are investigating if happier people are less likely to become obese.

Researchers will be looking at whether raising people's serotonin levels - the hormone that affects moods - would help them lose weight.

Group leader Dr Caroline Dalton said those lacking in serotonin often turned to food for a boost.

She said if that could be replaced by other activities it may stop them piling on the pounds.

'Fat gene'

The research, which will begin next month, is expected to last for 18 months.

Dr Dalton said she believed up to 75% of the population often craved food to improve their mood - and they could get a similar effect by doing exercise.

She said: "There are other ways to raise serotonin, such as exercise, so once people have been identified as having the 'fat gene,' they could be encouraged to become more active as a weight loss strategy.

"They would lose weight as they burned more calories, but they would also raise their serotonin levels, reducing their dependence on food as a way of improving mood."